This relates to the field of piezoelectric devices and, in particular, to piezoelectric cantilever devices.
Piezoelectric materials may be used to generate electrical energy when strain is applied to the piezoelectric material by external forces or vibrations. This electrical energy may be harnessed, for example, to charge a battery when the piezoelectric material is used to fabricate a piezoelectric generator or the electrical energy may be used, for example, to measure an applied force or to trigger the deployment of an automobile air bag when the piezoelectric material is used to fabricate an accelerometer sensor.
In many piezoelectric generator and sensor applications, a cantilever structure such as illustrated in FIGS. 1 and 2 is utilized.
In the example cantilever piezoelectric device illustrated in FIG. 1 the cantilever bar 24 is formed from a piezoelectric material which when flexed, generates an electrical voltage. An end of the piezoelectric bar 24 may be attached to the package 20 by support post 22. A proof mass 26 may be attached to the piezoelectric bar 24 to increase the amount of flex or strain to the piezoelectric bar when a force is applied to the package. A package lid 28 may seal the piezoelectric device into the package 20.
In the example cantilevered piezoelectric device illustrated in FIG. 2, the piezoelectric material 30 is sandwiched between a bottom electrode 32 and a top electrode 34. The bottom electrode 32, the top electrode 34, and the piezoelectric material 30 forms the cantilever piezoelectric device. As in the previous device, proof masses 26 may be attached to the cantilever to increase the amount of stress applied to the piezoelectric material 30 when a force is applied to the piezoelectric device. Lower support post 22 may attach an end of the lower electrode 32 to the package 20 and the upper support post 36 may attach a corresponding end of the upper electrode 34 to the package 20 or to a package lid 38.
The piezoelectric material is typically a ceramic material which may break causing the device to fail if too much force is applied. For example, the cantilever arm 24 in FIG. 1 may break if the piezoelectric device in FIG. 1 is dropped. Similarly the piezoelectric material 30 in FIG. 2 may crack causing the piezoelectric device to fail if the cantilever flex is excessive.